Telephone system.



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W. M. DAVIS. TELEPHONESYSTEM. (Applimion med Jun 17, 1901.) (lh: Nudel.)

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WILLIAM M. DAVIS, OF CHICAGO, ILLINOIS, ASSIGNOR TO STROMBERG- CARLSONTELEPHONE MANUFACTURING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OFILLINOIS.

TELEPHONE SYSTEM.

SEECIFICATION forming part of Letters Patent No. 715,999, dated December16, 1902.

Application filed June I7, 1901.

` To all whom it may concern:

Be it known that I, WILLIAM M. DAVIS, a citizen of the United States,residing at Chicago, in the county of Cook and State of Illi-` nois,have invented a certain new and useful Improvementin Telephone Systems,of which the following is a full, clear, concise, and eX- actdescription, reference being had to the accompanying drawings, forming apart of this specification.

My invention relates to telephony, and has for its object the provisionof improved cir cuit arrangements for telephone systems eml ployingprimary and secondary windings of transformers.

The invention relates particularly to that class of telephone systemswherein the receiver is included in a local secondary circuit with thesecondary winding. In practicing this form of telephony the primarywinding has usually been includeddirectly in the main line, as also thetransmitter,'bat.tery current having been usually supplied to thetransmitter and the primary winding over the telephone-line. The primarywinding has usually been of one-half-ohm resistance, while the receivercontained resistance to the amount of ninety ohms and the secondarywindingto the extent of sixty ohms, the secondary circuit having thusvastly more oh mic resistance than the primary winding. In practicing myinvention I increase the primary winding preferably to eleven ohms,A

which causes additional impedance in the circuit including the same. i

It is the object of my invention to counteract or nullify the impedancedue to the primary winding, which I accomplish by means of alow-resistance secondary circuit. This secondary circuit includes asecondary winding, which instead of being of high resistance-as, forexample, sixty ohms, according to the prior art-is greatly reduced,having, preferably, ten and one-half ohms. In order to maintain thissecondary circuit of as low resistance as possible, the receiverincluded therein is provided with two coils, each of fifty ohms,connected in parallel in the cir- Serial No. 64.854. (No model.)

has about thirty-live-and-one-half-ohms vresistance. This secondarycircuit by being of this low resistance, which is about one-fourth ofresistance usually employed in the prior art, serves to counteractimpedance due to the primary Winding. In order to get the 'necessarystrength of current and pressure in the secondary circuit that wouldotherwise be impaired by the reduced number of turns and resistance inthe secondary winding, the primary winding has its resistance and numyber of turns increased to maintain or produce the requiredtransformation. Thus are two important departures made from the practiceof the prior art-one the reduction of the resistance in the secondarycircuit, particularly the secondary winding therein, and the other anincrease over accepted practice in the length of wire" and number ofturns in the primary winding.

It is well known that a closed secondary circuit of high resistance willnot serve to reduce the impedance due toa coil in inductive relationtherewith. It is essential to have a secondary circuit or closed localcircuit of very low resistance. If it is sought to reduce the resistancein the secondary circuit by reducing the resistance of the secondarywinding, a difficulty is met in that with the arrangement of the priorart the required strength of transformation between the primary andsecondary windings is not retained.

Therefore after having reduced the resistance of the secondary Windingin accordance cuit. The secondary circuit thus in practice l Like partsare indicated by similar characters of reference throughout thedifferent Iigures.

I have omitted from the diagram all switching appliances, merelyillustrating the electrical condition of a circuit existing between twosubscribers that may be connected in well-known ways by well-knownapparatus at a central exchange.

I have indicated diagrammatically one type of telephone system, butother telephone systems may have my invention applied thereto.

In practicing my invention the resistance of the secondary circuit a,including the receiver b, is reduced at the receiver by including twocoils c c, each preferably of titty-ohms resistance, in parallel in thecircuit, the receiver thus presenting a resistance of twentyfive ohmsinstead of the higher resistance of ninety ohms or so with thearrangement of the prior art. To further reduce the resistance of thissecondary circuit, the secondary winding d has its resistance aboutone-fifth that which it was necessary to employ in the prior art, being,preferably, ten and one-half ohms. The secondary circuit thus organizedcreates suicient electromotive force to overcome or reduce the impedancedue to the primary winding. This secondary circuit thus greatly reducedin resistance, While sufficient to overcome the impedance due to theprimary winding, is not well adapted with the form of primary windingemployed in the prior art to provide the necessary strength oftransformation to secure effective operation of the receiver. I preferto secure the required current conditons iu the secondary circuit byincreasing the number of turns in the primary winding e and theresistance thereof, by which arrangement the required secondary of lowresistance is obtained without impairing the current conditions of thesecondary circuit, while at the same time removing the impedance. As aresult I am enabled to secure a transmission of voice-currents that isfar superior to results that have heretofore been secured, the receiversin the secondary circuits being rendered thereby much more sensitive tothe voice-currents, which have full effect thereupon because of theremoval of the impedance. A batterytransmitterfis included at the samesubstation with the corresponding Winding e. Two substations areillustrated, a common battery g being connected in multiple between thelines, impedance h being included in the same bridgewiththebattery.Theinduction-windings are preferably wound about a core i, one coilbeing superposed upon and inclosing the other. As the primary windinginaccordance with the preferred practice of my invention tends to creategreaterimpedance, this winding is preferably the one that issuperposed,be ing thereby further removed from the core to reduce thereactauce. The secondary winding, conversely, should have its reactanceincreased to counteract the impedance due to the primary winding, and onthis account it is placed next to the core. I have secured good resultsin practice by providing eight layers of No. 26 Brown 95 Sharpe gageWire for the secondary winding, having ten-and-onehalf-ohms resistanceand having two thousand five hundred and forty turns. The primarywinding may have six layers of No. 26 Brown a Sharpe gage, having aresistance of eleven ohms and having one thousand nine hundred turns.The receivers b are thus subject to the full fluctuating voice-currentsby reason of the absence of the connteracting impedance.

The main dierence between my present invention and the prior artconsists in the provision of a secondary receiver-circuit that is ofsuch a character as to overcome the impedance due to the primaryWinding, which result was not secured hitherto because of the very highresistance of the secondary circuit. As an additional difference betweenmy present invention and the prior art there is the provision of theprimary winding, that is adapted to compensate for the reducedresistance of the secondary winding to maintain and improve thenecessary electrical condition in the secondary circuit.

I believe it to be broadly new with me to provide the com bination, witha telephone receiver and transmitter, of primary and secondary windingshaving substantially the same resistance.

By means of my invention I have secured far superior results to thosethat have been obtained in commercial practice hitherto, and While Ihave particularly described the preferred embodiment of the invention Ido not wish to be limited thereto, as modications may be made withoutdeparting from the spirit thereof; but,

Having thus described my invention, I claim as new and desire to secureby Letters Patent- 1. In a telephone system, the combination with theprimary winding of an inductioncoil included in a telephonie circuit,ofa transmitter and battery in circuit therewith, and a secondarycircuit of low resistance including the secondary winding and atelephone-receiver, substantially as described.

2. In a telephone system, the combination with the primary winding of aninductioncoil included in a telephonie circuit, ofa transmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a low-resistancetelephone-receiver, substantially as described.

3. In a telephone system, the combination with the primary winding of aninductioncoil includedin a telephonie circuit, ofatransmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a low-resistancetelephone-receiver, the receiver having two coils connected in paralleland included in the secondary circuit, substantially as described.

4. .In a telephone system, the combination IOO IIO

with the primary winding of comparatively high resistance of aninduction-coil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit'including alow-resistance secondary winding and a low-resistancetelephone-receiver, the receiver having two coils connected in paralleland included in the secondary circuit, substantially as described.

5. In a telephone system, the combination with the primary winding ofcomparatively high resistance of an induction-coil included in atelephonic circuit, of a transmitter and battery in circuit therewith,and a secondary circuit including a low-resistance secondary winding anda telephone-receiver,the receiver having two coils connected in paralleland included in the secondary circuit, substantially as described.

6. In a telephone system, the combination with the primary winding of aninductioncoil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit of low resistanceincluding the secondary winding andV a telephone-receiver, the primaryand secondary windings being of substantially the same resistance,substantially as described.

7. In a telephone system, the combination with the primary winding of aninductioncoil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a low-resistance telephonereceiver, the prim ary and secondary windings being of substantially thesame resistance, substantially as described.

8. In a telephone syste1n,'the combination with the primary winding ofan inductioncoil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a seconday circuit including alow-resistance secondary winding and a low-resistancetelephone-receiver, the receiver having two coils connected in paralleland included in the second circuit, the primary and secondary windingsbeing of substantially the same resistance, substantially as described.

9. In a telephone system, the combination with the primary winding of aninductioncoil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including asecondary winding and a low-resistance telephonereceiver, the receiverhaving two coils connected in parallel and included in the secondarycircuit, the primary and secondary windings being of substantially thesame resistance, substantially as described.

10. In a telephone system, the combination with the primary winding ofan inductioncoil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including asecondary winding and a telephone-receiver, the receiver having twocoils connected in parallel and included in the secondary circuit, theprimary and secondary windings being of substantially the sameresistance, substantially as described.

l1. In a telephone system, the combination with the primarywinding of aninductioncoil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit of low resistanceincluding the secondary winding and a telephone-receiver, the primarywinding being superposed upon the secondary winding and surrounding thesame, these windings being placed about a common magnetic core,substantially as described.

12. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a low-resistancetelephone-receiver, the primary winding being superposed upon thesecondary winding and surrounding the same, these windings being placedabout a common magnetic core, substantially as described.

13. In a telephone system,'the combination with the primary winding ofan induction-coil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a low-resistancetelephone-receiver, the receiver having two coils connected in paralleland included in the secondary circuit, the primary winding beingsuperposed upon the secondary winding and surrounding the same, thesewindings being placed about a common magnetic core, substantially asdescribed.

14. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including asecondary winding and a low-resistance telephone-receiver, the receiverhaving two coils connected in parallel and included in the secondarycircuit, the primary winding being superposed upon the secondary windingand surrounding the same, these windings being placed about a commonmagnetic core, substantially as described.

15. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonic circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit includingasecondary winding and a telephone-receiver, the receiver having twocoils connected in parallel and included in the secondary circuit, theprimary winding being superposed upon the secondary wiuding andsurrounding the same, these windings being placed abouta common magneticcore, substantially as described.

16. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonic circuit, of a trans- IOO IIO

mittei` and battery in circuit therewith, and a secondary circuit of lowresistance including the secondary winding and a telephone-receiver, theprimary and secondary windings being of substantially the sameresistance, the primary winding being superposed upon the secondarywinding and surrounding the same, these windings being placed about acommon magnetic core, substantially as described.

17. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonie circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a lou/resistancetelephone-receiver, the primary and secondary windings being ofsubstantially' the same resistance, the primary winding being superposedupon the secondary winding and surrounding the same, these windingsbeing placed about a common magnetic core, substantially as described.

IS. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonie circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including alow-resistance secondary winding and a low-resistancetelephone-receiver, the receiver having two coils connected in paralleland included in the secondary circuit, the primary and secondarywindings being of substantially the same resistance, the primary windingbeing superposed upon the secondary winding and surrounding the same,these windings being placed about a common magnetic core, sub stantiallyas described.

19. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonie circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including asecondary winding and a low-resistance telephone-receiver, the receiverhaving two coils connected in parallel and included in the secondarycircuit, the primary and secondary windings being of substantially thesame resistance, the primary winding being superposed upon the secondarywinding and surrounding the same, these windings being placed about acommon magnetic core, substantially as described.

20. In a telephone system, the combination with the primary windingof aninduction-coil included in a telephonie circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including asecondary winding and a telephone-receiver, the receiver having twocoils connected in parallel and included in the secondary circuit, theprimary and secondary windings being of substantially the sameresistance, the primary winding being snperposed upon the secondarywinding and surrounding the same, these windings being placed about acommon magnetic core, substantially as described.

2l. In a telephone system, the combination with the primary winding ofan induction-coil included in a telephonie circuit, of a transmitter andbattery in circuit therewith, and a secondary circuit including thesecondary winding and a telephone-receiver and serving to create counterelectroinotive force to overcome impedance due to the primary winding,substantially as described.

22. The combination with the primary winding of an induction-coil ortransformer, of a battery and transmitter in closed circuit therewith, asecondary winding and a receiver in closed circuit therewith, the saidprimary and secondary windings approximating equality of resistance,substantially as described.

23. The combination with a primary Winding, of a battery and atransmitter in closed circuit therewith, of a secondary winding and areceiver in closed circuit therewith, the said primary and secondarywindings being of substantially thc same resistance, the primary windingbeing superposed upon and inclosing the secondary winding, both of thewindings being located upon a common core, substantially as described.

24. The combination with the primary winding of an induction-coil ortransformer of a battery and transmitter in closed circuit therewith, asecondary winding and a receiver in closed circuit therewith, the saidprimary and secondary windings being respectively and compared withprior telephone induction-coils ot' high and low resistance andapproximating the same resistance, substantially as described.

In witness whereof I hereunto subscribe my name this 23d day of May, A.D. 1901.

WILLIAM M. DAVIS.

Vitnesses:

GEORGE L. CRAGG, HERBERT F. OBERGEELL.

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